Medically intractable epilepsy is relatively common. Uncontrolled studies suggest that surgery for epilepsy leads to seizure control in a majority of selected epilepsy patients. However, the value of epilepsy surgery depends not only on seizure control but also on improvement in quality of life: physical function, social health, cognition, emotional well-being,role functioning, energy, pain, health perceptions, and overall quality of life. The goals of this study are: (1) to develop a standardized seizure classification system that corresponds most highly with patients' quality of life by evaluating relationships between quality of life measures and seizure outcomes cross-sectionally; (2) to evaluate changes in post-surgical seizure occurrence over time and effects on quality of life; (3) to evaluate the relationships between a set of proposed variables such as age and duration of epilepsy prior to surgery and quality of life and seizure outcome measures; and (4) to estimate the impact of surgical intervention by comparing quality of life and seizure outcomes in surgical patients with outcomes in a nonrandomized comparison group who did not undergo surgery. The study will be based on data collected prospectively on a cohort of 239 protocol patients followed for up to 15 years at UCLA. Two quality-of-life measures have been collected on 84 percent of these patients before and after surgery; a third, recently developed, quality-of-life instrument. was completed by 88 percent of all living patients in 1990. The reliability of these three measures in this cohort has been established. We propose to supplement this rich data base by abstracting detailed clinical information from the medical records, including year-by-year seizure occurrence, medications, age at onset and duration of epilepsy, and selected pre-operation noninvasive test results, among others. A standardized seizure classification system will be developed by classifying the cohort's seizure outcomes according to different classification models, then evaluating the relationship to quality of life at follow-up, adjusting for initial quality of life and other covariates. Patterns of seizure outcome over time postoperatively will be evaluated. Multivariate techniques will be used to analyze (1) longitudinal changes in quality-of-life measures and relationships between quality-of-life measures and seizure control, after adjustment for clinical casemix variables, and (2) the effect of surgical intervention with adjustment for confounders.